Feb 21 (Reuters) - Dish Network Corp on Wednesday said its online streaming service Sling TV added 160,000 subscribers in the fourth quarter, disclosing numbers for the first time and providing an overall figure of 2.21 million.

Dish has been losing customers for its legacy pay-TV service for nearly a decade as people move away from satellite TV packages to online streaming services such as Netflix Inc and Amazon.com Inc's Prime Video.

The total subscribers for Sling pales in comparison with Netflix's about 118 million worldwide or Amazon Prime Video's 40 million, but they have been accumulated from scratch in just two years at a time when other cable TV providers are struggling.

Dish had 14 million subscribers in January 2015 before it launched the initiative, which started $20 per-month Sling TV subscriptions with a slim bundle of channels to target younger consumers avoiding pricey cable and satellite subscriptions.

However, its loss of another 121,000 subscribers for Dish TV in the quarter meant revenue from its total 13.24 million users of both services fell.

Jefferies analyst Scott Goldman said Dish's average revenue per user of $84.63 was below his estimate of $85.71 and Wall Street estimate of $86.10.

New Street Research analyst Jonathan Chaplin said the results were "not great," but that the primary value of the satellite business is to provide cash flow while Chairman Charlie Ergen seeks to monetize the rights it has accumulated to radio frequencies.

Dish has spent billions buying up wireless airwaves, or spectrum, in recent years, making it a potential acquisition target for U.S. wireless carriers.

The company faces a Federal Communications Commission deadline to use the spectrum by 2021 to build its first wireless network.

"We continue to believe the most obvious buyer is (telecoms company) Verizon, as they have by far the least amount of spectrum per subscriber among the U.S. carriers, and by far the most value to lose from network congestion and a rise in churn," Chaplin said.